It's hard to tell from the pictures but it looks like the collar is still there, so that's good.
Look at the condition of the jaws. Replacements have to be custom made and fitted for each individual Parker. Look at the jaw alignment. Check for any cracks in the slide or the jaw towers. Especially where the dynamic jaw meets the slide, and around the front support shelf under the dynamic jaw. If there is any welding or brazing, be wary. Open and close it to see if there is any binding, that will give you an indication of the condition of the screw and nut.
Otherwise, it looks to be in decent condition.